In conventional CRT (Cathode Ray Tube) display devices, the contour emphasizing processing is carried out aiming at high picture quality implementation and high-pass characteristic compensation. The contour emphasizing circuit to carry out this contour emphasizing processing is, as shown in FIG. 1, composed of a Y/C separation circuit 10, a color demodulation circuit 12, a contour extracting circuit, phase adjustment circuits 16, 18 and 20, an adder 22 and a matrix circuit 24.
The Y/C separation circuit 10 separates a Y (luminance) signal and a C (color) signal from the composite video signal (for example, compound color television signal) input to an input terminal 26, and the color modulation circuit 12 separates a Y signal, an R-Y (color difference) signal and a B-Y (color difference) signal on the basis of a Y signal and a C signal.
The contour extracting circuit 14 extracts the contour component Ye which is a high-pass component of a video signal on the basis of an adder 22.
The matrix circuit 24 prepares a signal adding the contour component Ye to the R (red), G (green) and B (blue) signals, respectively, on the basis of (Y+Ye) signals added by the adder 22, an (R-Y) and a (B-Y) signal phase-adjusted by phase adjustment circuits 18 and 20. That is to say, the matrix circuit 24 prepares R+Ye, G+Ye and B+Ye on the basis of the operations in the following equations (1), (2) and (3). By outputting these R+Ye, G+Ye and B+Ye to the CRT display device by means of output terminals 28r, 28g and 28b, videos contour-emphasized by this CRT display device are displayed. EQU (R-Y)+(Y+Ye)=R+Ye (1) EQU (G-Y)+(Y+Ye)=G+Ye (2) EQU (B-Y)+(Y+Ye)=B+Ye (3)
(G-Y) in the above equation (2) is generated by the following equation (4).
In case a video contour-emphasized by the matrix type display device driven by digital video signals (for example, R, G and B signals) like PDP and LCD is displayed, each signal of (R+Ye), (G+Ye) and (B+Ye) obtained in output terminals 28r, 28g and 28b in FIG. 1 is output to the display device after being digitized by the A/D (analog/digital) conversion circuit. However, in such a prior example, in case a large amplitude signal is input to an input terminal 26, or in case the contour emphasizing quantity (or contour emphasizing coefficient, the description is omitted, as it is similar afterwards) is "large", there is a problem that the correct operation cannot be obtained over the dynamic range of the A/D conversion circuit.
For example, in case a large amplitude signal is input to the input terminal 26, by outputting a signal over the dynamic range of the A/D conversion circuit as shown at the left-hand side in FIG. 2(a) from output terminals 28r, 28g and 28b, there are problems that signals exceeding an upper conversion reference voltage value VRT (for example, 5 volts) in the dynamic range as shown at the right-hand in said figure (a) are cut, resulting in producing white crushing or signals under the lower conversion reference voltage value VRT (for example, 3 volts) in the dynamic range are cut, resulting in producing black crushing.
Further, in case the contour emphasizing quantity of the contour extracting circuit 14 is "large", there are problems that signals over the dynamic range of the A/D conversion circuit as shown at the left-hand side in FIG. 2(b) are cut, resulting in producing white crushing or signals under the lower conversion reference voltage value VRB are cut, resulting in producing black crushing.
The present applicant simultaneously proposes a contour emphasizing circuit as shown in FIG. 3 as a separate application to solve the above mentioned problems.
This contour emphasizing circuit shown in FIG. 3 is constituted by A/D conversion circuits 30r, 30g and 30b, a phase adjustment circuit 31 composed of line memories 31r, 31g and 31b, a signal processing circuit 32, contour adders 34r, 34g and 34b, a Y signal generation circuit 36, a contour extracting circuit 38, a gain controller 40 for the contour components and a coefficient multiplication circuit 42.
The contour extracting circuit 38 is constituted by first and second line memories 48 and 50, a vertical contour extracting circuit 52, a contour emphasizing frequency setting circuit 54, a horizontal contour extracting circuit 56, a contour synthesis circuit 62, a core ring circuit 64 and a gain controller 66.
Hence, analog R, G and B signals input to input terminals 44r, 44g and 44b are converted to digital signals by A/D conversion circuits 30r, 30g and 30b, phase-adjusted by the phase adjustment circuit 31, signal-processed by the signal processing circuit 32 and input to contour adders 34r, 34g and 34b. The Y signal generation circuit 36 generates Y signals from digital R, G and B signals, the contour extracting circuit 38 extracts contour components from Y signals, these contour components extracted are input to contour adders 34r, 34g and 34b through the gain controller 40 and the coefficient multiplication circuit 42, are added to original digital R, G and B signals, and supplied to the display device through output terminals 86r, 86g and 86b.
As described above, it has been designed by adding the contour components after converting the analog R, G and B signals to digital signals by A/D conversion circuits 30r, 30g and 30b, contour emphasizing components, unlike conventional examples, do not surpass the dynamic range of A/D conversion circuit. For this reason, when analog color video signals input to input terminals 44r, 44g and 44b of the contour emphasizing circuit in FIG. 3 are large amplitude signals, or even when the contour emphasizing quantity is "large", neither white crushing nor black crushing is produced when outputting digital R, G and B signals from the contour emphasizing circuit in FIG. 3 to the display device driven by digital video signals and displaying a contour emphasizing video.
However, since the contour extracting circuit 38 requires two line memories of first and second line memories 48 and 50, the contour emphasizing circuit shown in FIG. 3 had the following problems as shown in (a), (b) and (c).
(a) Since the line memory requires a number of gates (for example, when the memory capacity is of 1024.times.8 bits in the line memory, approximately 12,700 more or less), there is a problem that in proportion as the power consumption is made large, the cost comes to be high.
(b) In case it is realized by discrete parts, there is problem that the mounting area comes to be large.
(c) In case it is built in the LSI (Large Scale Integrated Circuit), there are problems that the circuit scale is made large, and the user usage domain comes to be narrow.
The present invention is performed taking into account problems as described above, in case a large amplitude signal is input or even in case a contour emphasizing quantity is "large", can display a contour emphasizing video without white crushing or black crushing by the display device driven by a digital video signal, as well as realizes a contour emphasizing circuit enabling the limiting of 1 piece of line memory required by the contour extracting circuit.